Historically, synthetic fibers for use in apparel, including polyester fibers, have generally been supplied to the textile industry for use in fabrics and garments with the object of more or less duplicating and/or improving on natural fibers. For many years, commercial synthetic textile filaments, such as were made and used for apparel, were mostly of deniers per filament (dpf) in a similar range to those of the commoner natural fibers; i.e., cotton and wool. More recently, however, polyester filaments have been available commercially in a range of dpf similar to that of natural silk, i.e. of the order of 1 dpf, and even in subdeniers, i.e., less than about 1 dpf, despite the increased cost. Various reasons have been given for the recent commercial interest in such lower dpfs, such as about 1 dpf, or even subdeniers.
Our so-called "parent application" (originally U.S. Ser. No. 07/647,371 filed Jan. 29, 1991, but now abandoned in favor of continuation-in-parts, and issued as U.S. Pat. No. 5,250,245, the disclosure of which is hereby incorporated herein by reference) is concerned with the preparation of fine filaments by a novel direct spinning/winding process, in contrast with prior processes of first spinning larger filaments of denier greater than 1 which then needed to be further processed, in a coupled or a separate (split) process involving drawing, to obtain the desired filaments of reduced denier with properties suitable for use in textiles. The fine filaments according to the parent application are "spin-oriented" fine filaments; that is, produced without drawing as "undrawn" filaments. The significance of this is discussed in the art and hereinafter. The undrawn filaments and yarn (bundles) are often referred to by the term "as-spun" to distinguish from drawn filaments. Such undrawn fine spin-oriented filaments according to the parent application have the capability to be drawn down to a finer dpf.
The polyester polymer used for preparing spin-oriented filaments of the parent application (and of this invention herein) is selected to have a relative viscosity (LRV) in the range about 13 to about 23, a zero-shear melting point (T.sub.M .degree.) in the range about 240 C. to about 265 C.; and a glass-transition temperature (T.sub.g) in the range about 40 C. to about 80 C. (wherein T.sub.M .degree. and T.sub.g are measured from the second DSC heating cycle under nitrogen gas at a heating rate of 20 C. per minute). The said polyester polymer is a linear condensation polymer composed of alternating A and B structural units, where the A's are hydrocarbylenedioxy units of the formula [--O--R'--O--] and the B's are hydrocarbylenedicarbonyl units of the formula [--C(O)--R"--C(O)--], wherein R' is primarily [--C.sub.2 H.sub.4 --], as in the ethylenedioxy (glycol) unit [--O--C.sub.2 H.sub.4 --O--], and R" is primarily [--C.sub.6 H.sub.4 --], as in the p-phenylenedicarbonyl unit [--C(O)--C.sub.6 H.sub.4 --C(O)--], such to provide, for example, at least about 85 percent of the recurring structural units as ethylene terephthalate, [--O--C.sub.2 H.sub.4 --O--C(O)--C.sub.6 H.sub.4 --C(O)--].
Suitable poly(ethylene terephthalate), herein denoted as PET or 2GT, base polymer may be formed by a DMT-process, e.g., as described by H. Ludewig in his book "Polyester Fibers, Chemistry and Technology", John Wiley and Sons Limited (1971), or by a TPA-process, e.g., as described in Edging U.S. Pat. No. 4,110,316.
Included are also copolyesters in which, some of the hydrocarbylenedioxy and/or hydrocarbylenedicarbonyl units are replaced with different hydrocarbylenedioxy and hydrocarbylenedicarbonyl units to provide enhanced low temperature disperse dyeability, comfort, and aesthetic properties. Suitable replacement units are disclosed, e.g., in Most U.S. Pat. No. 4,444,710 (Example VI), Pacofsky U.S. Pat. No. 3,748,844 (Col. 4), and Hancock, et al. U.S. Pat. No. 4,639,347 (Col. 3).
The polyester polymer may also be modified with ionic dye sites, such as ethylene-5-M-sulfo-isophthalate residues, where M is an alkali metal cation, such as sodium or lithium; for example, in the range of 1 to about 3 mole percent ethylene-5-sodium-sulfo-isophthalate residues may be added to provide dyeability of the polyester filaments with cationic dyestuffs, as disclosed by Griffing and Remington U.S. Pat. No. 3,018,272, Hagewood et al in U.S. Pat. No. 4,929,698, Duncan and Scrivener U.S. Pat. No. 4,041,689 (Ex. VI), and Piazza and Reese U.S. Pat. No. 3,772,872 (Ex. VII).
To adjust the dyeability or other properties of the spin-oriented filaments and the drawn filaments therefrom, some diethylene glycol (DEG) may be added to the polyester polymer as disclosed by Bosley and Duncan U.S. Pat. No. 4,025,592 and in combination with chain-branching agents as described in Goodley and Taylor U.S. Pat. No. 4,945,151.
Fine filaments of lower shrinkage may be obtained, if desired, by incorporating chain branching agents, on the order of about 0.1 mole percent, as described in part in Knox U.S. Pat. No. 4,156,071, MacLean U.S. Pat. No. 4,092,229, and Reese in U.S. Pat. Nos. 4,883,032, 4,996,740, and 5,034,174; and/or increasing polymer viscosity by about +0.5 to about +1.0 LRV units.
The yarn characteristics and test methods used herein are as in the parent application, and in Frankfort and Knox U.S. Pat. No. 4,134,882, Knox U.S. Pat. No. 4,156,071, and Knox and Noe U.S. Pat. No. 5,066,447, except as otherwise indicated; for instance, the relative disperse dye rate (RDDR) is normalized to 1 dpf, dry heat shrinkage (DHS) is measured at 180.degree. C. (unless otherwise indicated, e.g. in Example 16), and the lab relative viscosity (LRV) is defined according to Broaddus in U.S. Pat. No. 4,712,988 and is equal to about (HRV--1.2), where HRV is given in above-mentioned U.S. Pat. Nos. 4,134,882 and 4,156,071. The term elongation-to-break (E.sub.B) has generally been used, but the term "residual elongation" has also been used herein, and is equivalent.
According to the parent application there is provided a process for preparing spin-oriented undrawn polyester filaments that are subdenier, for example, in the range of about 0.2 to about 0.8 denier per filament (dpf). The following is a summary of the process of the parent application for preparation of polyester fine filament yarns:
(a) by melting and heating polyester polymer, described hereinbefore, to a temperature (T.sub.P) in the range of about 25 C. to about 55 C. above the apparent melting temperature (T.sub.M).sub.a, wherein, (T.sub.M).sub.a is defined, herein, by: (T.sub.M).sub.a =[T.sub.M .degree.+2.times.10.sup.-4 (L/D.sub.RND)G.sub.a ], where L is the length of the capillary and where D.sub.RND is the capillary diameter in centimeters (cm) for a round capillary, or, for a non-round capillary, where D.sub.RND is the calculated equivalent diameter of a round capillary of equal cross-section area A.sub.c (cm.sup.2); and where the apparent capillary shear rate G.sub.a (sec.sup.-1)=[(32/60)/3.14)(w/1.2195)/D.sub.RND.sup.3 ], w is the capillary mass flow rate (g/min), and the polyester melt density is taken herein as 1.2195 g/cm.sup.3);
(b) filtering the resulting polymer melt through inert medium sufficiently rapidly that the residence time (t.sub.r) is less than about 4 minutes, wherein, t.sub.r is defined by ratio (V.sub.F /Q), V.sub.F (cm.sup.3) being the free-volume of the filter cavity (filled with the inert filtration medium) and Q (cm.sup.3 /min) being the polymer melt volume flow rate through the filter cavity; and then extruding the filtered polymer melt through a spinneret capillary at a mass flow rate (w) in the range of about 0.07 to about 0.7 grams per minute (g/min), the capillary being selected to have a cross-sectional area, A.sub.c =(3.14/4)D.sub.RND.sup.2, in the range of about 125.times.10.sup.-6 cm.sup.2 (19.4 mils.sup.2) to about 1250.times.10.sup.-6 cm.sup.2 (194 mils.sup.2), and a length (L) and diameter (D.sub.RND) such that the L/D.sub.RND -ratio is in the range of about 1.25 to about 6 (preferably 1.25 to about 4);
(c) protecting the freshly extruded polymer melt from direct cooling, as it emerges from the spinneret capillary, over a distance L.sub.DQ of at least about 2 cm and less than about 12(dpf).sup.1/2 cm, and then carefully cooling the extruded melt to below the polymer glass-transition temperature (T.sub.g) by use of laminar cross-flow air or by radially directed air of velocity (V.sub.a) in the range of about 10 to about 30 m/min; and attenuating the cooling spinline to an apparent spinline strain, defined as the natural logarithm (ln) of the ratio of the withdrawal speed (V) and the capillary extrusion speed (V.sub.o), in the range of about 5.7 to about 7.6, and developing during attenuation an apparent internal spinline stress at the "neck-point" in the range of about 0.025 to about 0.195 g/d;
(d) converging the cooled and fully attenuated filaments into a multifilament bundle by use of a low friction surface, such as by a metered finish tip applicator, at a distance (L.sub.c) from the face of the spinneret preferably in the range of about 50 cm to about [50+90(dpf).sup.1/2 ] cm, wherein the finish is usually an aqueous emulsion and percent finish-on-yarn is selected for end-use processing requirements; and then interlacing the filament bundle using an air jet where the degree of interfilament entanglement is selected based on yarn packaging and end-use requirements; and winding up the multifilament bundle at a withdrawal speed (V.sub.s), herein defined as the surface speed of the first driven roll, in the range of about 2 to about 6 km/min, wherein the retractive forces from aerodynamic drag are reduced by relaxing the spinline between the first driven roll and the windup roll.
According to the parent application, the following filament yarns are provided:
(a) spin-oriented polyester fine filaments of denier about 0.2 to about 0.8, a shrinkage differential (DHS-S) less than about +2%; a maximum shrinkage tension, (ST.sub.max) less than about 0.2 g/d; temperature of maximum shrinkage tension, T(ST.sub.max), between about (T.sub.g +5 C.) and about (T.sub.g +30 C.); a tenacity-at-7%-elongation (T.sub.7) in the range of about 0.5 to about 1.75 g/d and a [(T.sub.B).sub.n /T.sub.7 ])-ratio at least about (5/T.sub.7); and the percent elongation-at-break (E.sub.B) between about 40 and 160%.
(b) spin-oriented fine filaments, especially suitable as use as draw feed yarns (DFY), are further characterized by: boil-off shrinkage (S) and dry heat shrinkage (DHS) greater than about 12% and less than about the maximum shrinkage potential S.sub.m and an E.sub.B in the range of about 80% to about 160% with a T.sub.7 in the range of about 0.5 to about 1 g/d;
(c) spin-oriented fine filaments, especially suitable for use as direct-use yarns (DUY), are further characterized by: boil-off shrinkage (S) and dry heat shrinkage (DHS) in the range of about 2% to about 12%, such that the filament denier after boil-off, dpf(ABO), is in the range of about 1 to about 0.2 dpf; a T.sub.7 about 1 to about 1.75 g/d with an E.sub.B in the range of about 40% to about 90% and a post-yield modulus (M.sub.py) in the range of about 2 to about 12 g/d.
(d) drawn yarns of the spin-oriented filaments of this invention are characterized by an E.sub.B in the range of about 15% to about 55%, a dpf(ABO) of 1 or less, S between about 3 and about 12%, T.sub.7 greater than about 1 g/d, a [(T.sub.B).sub.n /T.sub.7 ])-ratio at least about (5/T.sub.7); and preferably a M.sub.py in range of about 5 to about 25 g/d and an RDDR value at least about 0.1.
The low shrinkage filaments of the parent application are further characterized by a fiber structure described in terms of: a dynamic loss modulus peak temperature, T(E"max) less than about 115 C.; an average crystal size (CS), between about 50 and about 90 angstroms (.ANG.) with a fractional volume crystallinity (X.sub.v) between about 0.2 and about 0.5 for density values between about 1.355 and about 1.395 grams/cm.sup.3 ; a fractional average orientation function (f) between about 0.25 and about 0.5 with a fractional amorphous orientation function (f.sub.a) less than about 0.4 such to provide an amorphous free-volume (V.sub.f,am) of at least about 0.5.times.10.sup.6 cubic angstroms (.ANG..sup.3).